(a) Field of the Invention
The present invention relates to a relaying apparatus in a gigabit passive optical network and a relaying method using the same.
(b) Description of the Related Art
A passive optical network (PON) technology is one of fiber to the home (FTTH) technologies proposed to effectively supply a bandwidth required for a subscriber terminal. The PON technology is classified into TDM-PON using a time division multiplexing (TDM) method and WDM-PON using a wavelength division multiplexing (WDM) method. The TDM-PON includes broadband PON (BPON), Ethernet PON (EPON), and gigabit PON (GPON), as examples. The BPON provides an asynchronous transfer mode (ATM) service as a method that is standardized by the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) G.983.x. The BPON is not suitable for an internet protocol (IP)-based service, and provides a bandwidth of 622 Mb/s (megabits per second) at a maximum. The EPON provides only an Ethernet service as a method that is standardized by the Institute of Electrical and Electronics Engineers (IEEE) 802.3ah. The EPON provides a bandwidth of the maximum uplink/downlink of 1.25 Gb/s (gigabits per second). The GPON provides a maximum uplink bandwidth of 1.244 Gb/s and a downlink bandwidth of 2.488 Gb/s as a method that is standardized by the ITU-T G.984.x in order to solve a problem of the bandwidth of the BPON and receive various multi-protocols, for example, ATM, TDM (time division multiplexing), and Ethernet service. In recent years, an optical network has been required to provide a bandwidth of 1 Gb/s or more in order to provide various multimedia contents, for example, IPTV (IP television), VoD (video on demand), games, etc. to subscribers, and the GPON satisfying this is in the limelight.
The GPON can service a maximum transmission distance of 20 Km as a point to multipoint network structure to share one optical line terminal (OLT) through a splitter in which 64 optical network units (ONUs) are passive elements. In general, the OLT is positioned at a central office and the ONU is positioned in a subscriber's home or a subscriber's terminal box. In the GPON, since a plurality of subscribers share the bandwidth through a time domain, the bandwidth that the subscribers can use is reduced as the number of subscribers increases. Accordingly, the GPON is suitable for a small-sized network and is not suitable for a large-sized network having hundreds of subscribers or more.
In recent years, as extension of a service area has been an issue, a method that is capable of servicing a transmission distance of 60 Km has been evaluated. For this, the long-reach PON (LR-PON) based on the GPON, which provides a long-reach service to a remote node of a trunk optical fiber section by using an active element-based relaying apparatus, has been standardized in the ITU-T G.984.6. In the LR-PON, since the number of central offices can be reduced, it is possible to save management and maintenance costs of the network.
Meanwhile, the WDM-PON that is one of the PON technologies provides service to subscribers in different wavelengths. Since a bandwidth of 1 Gb/s per wavelength is provided, each subscriber can receive a bandwidth of 1 Gb/s. However, since there are few services using a wide bandwidth, the WDM-PON has comparatively poorer bandwidth using efficiency than the GPON. Further, since the WDM-PON has light sources (laser diode, LD) having different wavelengths for each subscriber, the implementation cost of the WDM-PON is high and it is difficult to manage the WDM-PON.
Therefore, a hybrid GPON structure applying the WDM-PON to a relaying trunk network section of the GPON is being researched. In the hybrid GPON, optical signals having a single wavelength outputted from each OLT port are converted into a plurality of wavelengths through the WDM-PON and transmitted through a long-reach single trunk optical fiber. Each of the transmitted optical signals are separated from the remote node and thereafter converted into an optical signal having a single wavelength and transmitted to the ONUs. That is, ONUs of a maximum 64 branches can receive the single wavelength. Accordingly, the hybrid GPON can solve a problem in the bandwidth using efficiency of the WDM-PON and can provide a service to a large number of subscribers by using the single trunk optical fiber. Further, since different light sources are used for each ONU group, it is possible to save implementation cost of a large-scale network at the time of implementing the large-scale network. Accordingly, the hybrid GPON is suitable for construction of a large-scale network and long-reach transmission.
FIG. 1 is a diagram showing a known wavelength division multiplexing/time division multiplexing (WDM/TDM) hybrid optical network.
Referring to FIG. 1, the WDM/TDM hybrid optical network includes TDM-PONs 100, 130, and 140, a hybrid OLT 110, and a hybrid relaying apparatus 120. The TDM-PON includes a TDM-PON OLT 100, a splitter 130, and a TDM-PON ONU 140. The TDM-PON includes N TDM-PON OLTs 100 and N splitters 130 corresponding thereto, and includes a plurality of TDM-PON ONUs 140 branched from each splitter 130. The hybrid OLT 110 includes a TDM-PON optical transceiver (TDM-PON TRx) 111, a WDM-TDM matcher (WTA) 112, a WDM-PON optical transceiver (WDM-PON TRx) 113, and a WDM wavelength branching multiplexer (WDM MUX) 114. Each of the TDM-PON optical transceiver 111, the WDM-TDM matcher 112, and the WDM-PON optical transceiver 113 of the hybrid OLT 110 may be provided in N numbers to correspond to N TDM-PON OLTs 100. The hybrid relaying apparatus 120 includes a WDM wavelength branching multiplexer (WDM MUX) 124, a WDM-PON optical transceiver (WDM-PON TRx) 123, a WDM-TDM matcher (WTA) 122, and a TDM-PON optical transceiver (TDM-PON TRx) 121. Each of the TDM-PON optical transceiver 123, the WDM-TDM matcher 122, and the TDM-PON optical transceiver 121 of the hybrid relaying apparatus 120 may be provided in N numbers to correspond to N TDM-PON OLTs 100. The hybrid OLT 110 may be positioned at the central office and the hybrid relaying apparatus 120 may be positioned at the remote node RN. The hybrid OLT 110 and the hybrid relaying apparatus 120 enable long-reach transmission and high branching in comparison with the known TDM-PON, for example, the GPON.
In downlink transmission, an optical signal of λdT is transmitted to the TDM-PON optical transceiver 111 of the hybrid OLT 110 from the TDM-PON OLT 100 and is converted into an electrical signal, and the WDM-TDM matcher 112 matches the electrical signal with the WDM-PON optical transceiver 113. N WDM-PON optical transceivers 113 generate optical signals having different wavelengths λd1, λd2, . . . , λdN from the electrical signal, and one WDM wavelength branching multiplexer 114 connected with N WDM-PON optical transceivers 113 multiplexes the optical signals having different wavelengths and transmits them to the hybrid relaying apparatus 120. The WDM wavelength branching multiplexer 124 of the hybrid relaying apparatus 120 branches the optical signals having different wavelengths. N WDM-PON optical transceivers 123 convert the optical signals having different wavelengths into the electrical signal, and the WDM-TDM matcher 122 matches the electrical signal with the TDM-PON optical transceiver 121. The TDM-PON optical transceiver 121 converts the electrical signal into the optical signal of λdT. The splitter 130 transmits the optical signal of λdT to the plurality of TDM-PON ONUs 140 branched from the splitter 130.
In uplink transmission, an optical signal of λuT is transmitted to the TDM-PON optical transceiver 121 of the hybrid relaying apparatus 120 from the TDM-PON ONU 140 and is converted into the electrical signal, and the WDM-TDM matcher 122 matches the electrical signal with the WDM-PON optical transceiver 123. N WDM-PON optical transceivers 123 generate optical signals having different wavelengths λu1, λu2, . . . , λuN from the electrical signal, and the WDM wavelength branching multiplexer 124 multiplexes the optical signals having different wavelengths and transmits them to the hybrid OLT 110. The WDM wavelength branching multiplexer 114 of the hybrid OLT 110 branches the optical signals having different wavelengths. N WDM-PON optical transceivers 113 convert the optical signals having different wavelengths into the electrical signal, and the WDM-TDM matcher 112 matches the electrical signal with the TDM-PON optical transceiver 111. The TDM-PON optical transceiver 111 converts the electrical signal into the optical signal of λUT. The optical signal of λuT is transmitted to the TDM-PON OLT 100.
The WDM/TDM hybrid optical network shown in FIG. 1 enables a high branching rate and long-reach transmission in comparison with the TDM-PON or WDM-PON. However, the optical signal that the TDM-PON ONU 140 uplink-transmits is transmitted in a burst in accordance with the TDM method. Therefore, the hybrid relaying apparatus 120 needs a control signal for converting a burst optical signal into the electrical signal. Further, in the section using the WDM-PON technology, the optical signal is continuously transmitted, but when the optical signal is transmitted in the burst like the known WDM-TDM hybrid optical network, an error may be generated. Further, since the WDM-TDM matcher 122 of the hybrid relaying apparatus 120 provides only a matching function using the electrical signal, an additional device and an additional channel are required to collect state monitoring information of the TDM-PON optical transceiver 121 and the WDM-PON optical transceiver 123 of the hybrid relaying apparatus 120. System complexity is increased due to the additional device and channel.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.